U.S. patent application number 14/522950 was filed with the patent office on 2015-05-14 for variable neutral impedance for multi-source system.
The applicant listed for this patent is Eaton Corporation. Invention is credited to Daniel Patrick O'Reilly, David Doyle Shipp.
Application Number | 20150130280 14/522950 |
Document ID | / |
Family ID | 53043181 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150130280 |
Kind Code |
A1 |
O'Reilly; Daniel Patrick ;
et al. |
May 14, 2015 |
VARIABLE NEUTRAL IMPEDANCE FOR MULTI-SOURCE SYSTEM
Abstract
A system includes a first power source and a variable neutral
impedance circuit configured to vary a neutral impedance of the
first power source based on presence and absence of a parallel
coupling of the first power source with a second power source. The
variable neutral impedance circuit may be configured to reduce a
neutral current of the first power source when the first power
source is operating in parallel with the second power source. The
variable neutral impedance circuit may include an impedance coupled
in series with the first power source, a bypass switch configured
to bypass the impedance and a control circuit configured to control
the bypass switch. The impedance may include a resistor.
Inventors: |
O'Reilly; Daniel Patrick;
(Monroeville, PA) ; Shipp; David Doyle;
(Murrysville, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Eaton Corporation |
Cleveland |
OH |
US |
|
|
Family ID: |
53043181 |
Appl. No.: |
14/522950 |
Filed: |
October 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61901697 |
Nov 8, 2013 |
|
|
|
Current U.S.
Class: |
307/65 ; 307/72;
307/80 |
Current CPC
Class: |
H02J 9/066 20130101;
H02J 3/38 20130101 |
Class at
Publication: |
307/65 ; 307/80;
307/72 |
International
Class: |
H02J 9/06 20060101
H02J009/06; H02J 3/38 20060101 H02J003/38 |
Claims
1. A system comprising: a first power source; and a variable
neutral impedance circuit configured to vary a neutral impedance of
the first power source based on presence and absence of a parallel
coupling of the first power source with a second power source.
2. The system of claim 1, wherein the variable neutral impedance
circuit is configured to reduce a neutral current of the first
power source when the first power source is operating in parallel
with the second power source.
3. The system of claim 1, wherein the variable neutral impedance
circuit comprises: an impedance coupled in series with the first
power source; a bypass switch configured to bypass the impedance;
and a control circuit configured to control the bypass switch.
4. The system of claim 3, wherein the impedance comprises a
resistor.
5. The system of claim 1, wherein the first and second power
sources comprise respective first and second backup generators.
6. The system of claim 5, wherein the first and second generators
have different pitches.
7. The system of claim 1, wherein the second power source comprises
a utility power source.
8. A system comprising: a first generator and a second generator
configured to be coupled in parallel; and a variable neutral
impedance circuit configured to change a neutral impedance of the
first generator responsive to a status of a connection between the
first generator and the second generator.
9. The system of claim 8, wherein the variable neutral impedance
circuit is configured to provide a first neutral impedance when the
first and second generators are operating in parallel and to
provide a second neutral impedance when the first generator is
operating independently of the second generator.
10. The system of claim 8, wherein the first and second generators
comprise respective backup generators configured to provide power
in the event of failure of a utility source.
11. The system of claim 1, wherein the variable neutral impedance
circuit comprises: an impedance coupled in series with the first
generator; a bypass switch configured to bypass the impedance; and
a control circuit configured to control the bypass switch.
12. The system of claim 11, wherein the impedance comprises a
resistor.
13. The system of claim 8, wherein the first and second generators
have different pitches.
14. A method comprising: providing a first neutral impedance for a
first power source when the first power source is operating in
parallel with second power source; and providing a second neutral
impedance for the first power source when the first power source is
operating independently of the second power source.
15. The method of claim 14, wherein the first neutral impedance is
configured to reduce a neutral current of the first power source
when the first power source is operating in parallel with the
second power source.
16. The method of claim 14: wherein providing a first neutral
impedance for a first power source when the first power source is
operating in parallel with second power source comprises providing
a circuit component in series with neutral terminal of the first
power source and; wherein providing a second neutral impedance for
the first power source when the first power source is operating
independently of the second power source comprises bypassing the
circuit component.
17. The method of claim 16, wherein the circuit component comprises
a resistor.
18. The method of claim 14, wherein the first and second power
sources comprise respective first and second backup generators.
19. The method of claim 14, wherein the second power source
comprises a utility power source.
Description
RELATED APPLICATION
[0001] The present application claims priority from U.S.
Provisional Application No. 61/901,697 entitled "VARIABLE NEUTRAL
IMPEDANCE FOR MULTI-GENERATOR SYSTEM," filed on Nov. 8, 2013 and
incorporated herein by reference in its entirety.
BACKGROUND
[0002] The inventive subject matter relates to power systems and
methods of operating the same and, more particularly, to
multi-source power systems and methods and operating the same.
[0003] Some power system applications use multiple generators
configured to serve a load in parallel. For example, in data center
applications, a set of parallel connected emergency backup
generators may be used to supply power to equipment in the event of
a failure of a utility power supply. If such generators each have
low impedance ground connections and do not have the same winding
pitch design, significant third harmonic currents might be
generated in the neutral conductors of some of the generators. Such
ground current may cause unwanted tripping of switchgear or
protective devices, generator control malfunction and may require
derating of some of the generators.
SUMMARY
[0004] Some embodiments of the inventive subject matter provide a
system including a first power source and a variable neutral
impedance circuit configured to vary a neutral impedance of the
first power source based on presence and absence of a parallel
coupling of the first power source with a second power source. The
variable neutral impedance circuit may be configured to reduce a
neutral current of the first power source when the first power
source is operating in parallel with the second power source.
[0005] In some embodiments, the variable neutral impedance circuit
may include an impedance coupled in series with the first power
source, a bypass switching device configured to bypass the
impedance and a control circuit configured to control the bypass
switching device. The impedance may include a resistor.
[0006] In some embodiments, the first and second power sources may
include respective first and second backup generators. The first
and second generators may have different winding pitches. In
further embodiments, the second power source may include a utility
power source.
[0007] Further embodiments of the inventive subject matter provide
a system including a first generator and a second generator
configured to be coupled in parallel and a variable neutral
impedance circuit configured to change a neutral impedance of the
first generator responsive to a status of a connection between the
first generator and the second generator. The variable neutral
impedance circuit may be configured to provide a first neutral
impedance when the first and second generators are operating in
parallel and to provide a second neutral impedance when the first
generator is operating independently of the second generator.
[0008] Methods according to some embodiments including providing a
first neutral impedance for a first power source when the first
power source is operating in parallel with at least one second
power source and providing a second neutral impedance for the first
power source when the first power source is operating independently
of the at least one second power source. The first neutral
impedance may be configured to reduce a circulating neutral current
of the first power source when the first power source is operating
in parallel with the at least one second power source. Providing a
first neutral impedance for a first power source when the first
power source is operating in parallel with the at least one second
power source may include providing a circuit component in series
with neutral terminal of the first power source and providing a
second neutral impedance for the first power source when the first
power source is operating independently of the at least one second
power source may include bypassing the circuit component. The
circuit component may include a resistor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 illustrates a power system according to some
embodiments of the inventive subject matter.
[0010] FIG. 2 illustrates an example of relay logic for
implementation of the power system of FIG. 1 according to further
embodiments.
DETAILED DESCRIPTION
[0011] Specific exemplary embodiments of the inventive subject
matter now will be described with reference to the accompanying
drawings. This inventive subject matter may, however, be embodied
in many different forms and should not be construed as limited to
the embodiments set forth herein; rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the inventive subject matter to
those skilled in the art. In the drawings, like numbers refer to
like elements. It will be understood that when an element is
referred to as being "connected" or "coupled" to another element,
it can be directly connected or coupled to the other element or
intervening elements may be present. As used herein the term
"and/or" includes any and all combinations of one or more of the
associated listed items.
[0012] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the inventive subject matter. As used herein, the singular forms
"a", "an" and "the" are intended to include the plural forms as
well, unless expressly stated otherwise. It will be further
understood that the terms "includes," "comprises," "including"
and/or "comprising," when used in this specification, specify the
presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, integers, steps, operations, elements,
components, and/or groups thereof.
[0013] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
inventive subject matter belongs. It will be further understood
that terms, such as those defined in commonly used dictionaries,
should be interpreted as having a meaning that is consistent with
their meaning in the context of the specification and the relevant
art and will not be interpreted in an idealized or overly formal
sense unless expressly so defined herein.
[0014] FIG. 1 illustrates a power system according to some
embodiments. The power system includes first, second, and third
generators 20-1, 20-2, 20-3, which are configured to be coupled to
a bus 10 by respective breakers G1, G2, G3. The generators 20-1,
20-2, 20-3 may be, for example, a set of emergency backup
generators used to supply power to the bus 10 in the event of a
failure of a utility power supply. It will be appreciated that, in
some embodiments, more than three generators may be used.
[0015] The first, second and third generators 20-1, 20-2, 20-3 may
have different winding pitches. For example, the first and second
generators 20-1, 20-2 may be 2/3rd pitch generators, while the
third generator 20-3 may be a th pitch generator. Consequently, if
the first generator 20-1 and/or the second generator 20-2 were to
be coupled to ground using a low-impedance connection while coupled
to the bus 10 in parallel with the third generator 20-3,
significant third harmonic currents will be generated by the th
pitch generator 20-3 diving circulating third harmonic currents in
the neutral conductors of the 2/3rd pitch generators 20-1, 20-2.
This could result in ground fault currents that might cause
unwanted tripping of switchgear. The third harmonic currents might
also necessitate derating of the 2/3rd pitch generators 20-1,
20-2.
[0016] According to some embodiments, such third harmonic currents
may be reduced by placing resistors R1, R2 in the neutral paths of
the 2/3rd pitch generators 20-1, 20-2 when either of these
generators is coupled in parallel with the th pitch generator 20-3.
The resistors R1, R2 may limit neutral currents and thus maintain
normal operation within switchgear short circuit ratings. Because
the th pitch generator 20-3 is directly grounded, line-to-neutral
(single phase) loads may be properly served. According to further
aspects, the resistors R1, R2 may be bypassed when either or both
of the 2/3rd pitch generators 20-1, 20-2 is being operated with the
th pitch generator 20-3 disconnected from the bus 10. As shown,
such bypassing may be accomplished using, for example, motorized
switches S1, S2. Bypassing the neutral resistor R1 or the neutral
resistor R2 enables the corresponding first generator 20-1 or
second generator 20-2 to properly supply single phase loads. A
control circuit 30 may be configured to control the motorized
switches S1, S2 responsive to a state of the th pitch generator
20-3. The control circuit 30 may include any of a variety of
different arrangements of analog circuitry and/or digital
circuitry, and may be configured to control and/or operate
responsive to various components of the power system.
[0017] It will be appreciated that the above-describe techniques
may be used in applications in which local generators (e.g.,
engine-generator sets) are operated in parallel with a utility
source. For example, in some embodiments, the first generator 20-1
may be a Y-connected transformer coupled to a utility grid, while
the second and third generators 20-2, 20-3 are local
generators.
[0018] FIG. 2 illustrates relay logic that may be used in such a
control circuit according to some embodiments. Referring to the
left side of the figure, starting at a state in which the th pitch
generator 20-3 is disconnected from the bus (contact G3a of the
breaker G3 open) and the first 2/3rd pitch generator 20-1 is
connected to the bus 10 via the breaker G1 and the motorized switch
S1 for the first generator 20-1 is closed, closure of the breaker
G3 to connect the th pitch generator 20-3 to the bus 10 results in
opening of the motorized switch S1, removing the bypass around the
resistor R1 in the neutral path of the first 2/3rd pitch generator
20-1. A similar logic applies if the second 2/3rd pitch generator
20-2 is operating and the th pitch generator 20-3 is brought on
line. If the th pitch generator 20-3 is decoupled from the bus 10
by opening the breaker G3 while either of the first and second
2/3rd pitch generators 20-1, 20-2 is still connected to the bus 10,
the corresponding switch S1 and/or the switch S2 is closed, causing
the neutral resistor R1 and/or the neutral resistor R2 to be
bypassed.
[0019] It will be appreciated that the relay-based implementation
shown in FIG. 2 is provided for purposes of illustration, and that
other types of control circuitry may be used to similar effect in
other embodiments. For example, control logic along the lines
illustrated in FIG. 2 may be implemented using a programmable logic
controller (PLC) or other computer-based control circuitry. It will
be further appreciated that other bypassable impedances may be used
for neutral connections along the lines discussed above, for
example, combinations of resistors with other elements, such as
inductors.
[0020] Embodiments of the inventive subject matter may provide
several advantages. For example, some embodiments of the inventive
subject matter may facilitate use of combinations of generators
having different pitches and reduce or eliminate the need to derate
generators in such applications.
[0021] In the drawings and specification, there have been disclosed
exemplary embodiments of the inventive subject matter. Although
specific terms are employed, they are used in a generic and
descriptive sense only and not for purposes of limitation, the
scope of the inventive subject matter being defined by the
following claims.
* * * * *